<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <style>
        *{
            margin:0;
            padding: 0;
        }
        .main{
            float: left;
            width: 100%;

        }
        .main .main-content{
            margin: 0 210px;
            background-color: rgba(33, 114, 214, 0.8);
            height: 500px
        }
        .left{
            width: 200px;
            float: left;
            background-color: rgba(255, 82, 0, 0.8);
            margin-left: -100%;
            height: 200px

        }
        .right{
            width: 200px;
            height: 200px;
            margin-left: -200px;
            float: left;
            background-color: rgba(90, 243, 151, 0.8);
        }
    </style>
    <title>二、margin为负值的常见布局应用</title>
</head>
<body>
    <!-- 左右固定，中间自适应（双飞翼） -->
    <div class="main">
        <div class="main-content">main content</div>
    </div>
    <div class="left">left</div>
    <div class="right">right</div>
</body>
</html>